1. Field of Invention
The invention relates generally to current generators, and more particularly, to spin current generators for spintronics applications.
2. Description of Related Art
This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light and not as admissions of prior art.
The development of microelectronics has led to large increases in integration density and efficiency. However, the conventional electronic methods of operation by applying voltage to control electron charge are fundamentally limited. Further improvements in nonvolatility, speed, and size of electronic devices may require advancements in new technology. Spintronics, or spin electronics (also known as spin transport electronics and magnetoelectronics), refers to the study of the spin of an electron in solid state physics and the possible devices that may advantageously use electron spin properties instead of, or in addition to, the conventional use of electron charge.
The spin of an electron has two states and is characterized as being either “spin up” or “spin down.” Conventional spintronics devices have relied on systems that provide bidirectional current to alter the electron spins in the device. For example, one spintronics application involves data storage through a spintronics effect known as giant magnetoresistance (GMR). The GMR structure includes alternating ferromagnetic and nonmagnetic metal layers, and the magnetizations and electron spins in each of these magnetic layers provide resistance changes through the layers. The resistance of the GMR may change from low (if the magnetizations are parallel) to high (if the magnetizations are antiparallel), and the inducing and detecting of such magnetoresistance changes are the basis for writing and reading data. Another example of spintronics devices includes spin torque transfer magnetic random access memory (STT-MRAM). STT-MRAM also exploits electron spin polarity by utilizing the electron spin to switch the magnetization of ferromagnetic layers to provide two programmable states of low and high resistance.
This alteration of magnetization typically employs a bidirectional programming current to change the magnetizations of the layers in a memory cell. However, bidirectional programming logic requires more cell space. A transistor select device is required for each memory cell, and this also increases the cell area. Furthermore, bidirectional programming logic is generally more complicated and less efficient than unidirectional programming logic.